Single Impurity Effects in Multiband Superconductors with Different Sign Order Parameters

TL;DR

This paper investigates the effects of single and multiple impurities in multiband s-wave superconductors with sign-changing order parameters, revealing impurity-induced bound states and implications for experimental detection.

Contribution

It provides an exact formulation of impurity-induced bound state energies considering both intra- and interband scattering in +-s-wave superconductors, enhancing understanding of impurity effects.

Findings

Impurity-induced bound states are close to the impurity site.

Interband scattering destabilizes the Kondo singlet in magnetic impurities.

Local density of states around impurities can be probed by NMR.

Abstract

A single impurity problem is investigated for multiband s-wave superconductors with different sign order parameters (+-s-wave superconductors) suggested in Fe-pnictide superconductors. Not only intraband but also interband scattering is considered at the impurity. The latter gives rise to impurity-induced local boundstates close to the impurity. We present an exact form of the energy of the local boundstates as a function of strength of the two types of impurity scattering. The essential role of the impurity is unchanged in finite number of impurities. The main conclusions for a single impurity problem help us understand effects of dense impurities in the +-s-wave superconductors. Local density of states around the single impurity is also investigated. We suggest impurity site nuclear magnetic resonance as a suitable experiment to probe the local boundstates that is peculiar to the +-s-wave state. We find that the +-s-wave model is mapped to a chiral dx2-y2+-idxy-wave, reflecting the unconventional nature of the sign reversing order parameter. For a quantum magnetic impurity, interband scattering destabilizes the Kondo singlet.